The fetal phase of prenatal development lasts from nine weeks after fertilization to birth (usually at around 38 weeks).
With the formation of all organ systems (though only in a rudimentary form) already behind it,
the fetus now has two primary tasks during this final phase of prenatal development:
a. Continued development of organ systems—each system must mature and eventually begin functioning in preparation for birth.
b. Continued overall body growth—the overall size of the fetus will increase by twenty fold during these few months, as shown in this illustration.
Arms and legs will grow dramatically, and before long, the head will no longer seem so disproportionate, compared with the rest of the body.
During the fetal phase, overall size increases dramatically—from 1 gram (1/450th of a pound)
and 2.5 centimeters (1 inch) at 9 weeks to 3000 grams (7 pounds) and 50 centimeters (20 inches) at 38 weeks!